Partable Thermal Heat Pipe

ABSTRACT

A heat pipe for conducting heat away from an electronic device attached to a removable electronic module includes two self-aligning sections. A source section is attached to the removable electronic module and a target section passes through and is retained by a fixed member. One end of the source section is in thermal contact with a heat source and the other end includes a self aligning female thermal interface. One end of the target section includes a self aligning male thermal interface and the other end includes a heat sink. The female end of the source section and the male end of the target section are moved into contact with each other to form a thermal connection that permits heat from the heat source to be transferred to the heat sink.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Patent Application No. 61/200,717 filed Dec. 3, 2008, which application is incorporated herein by references in its entirety.

BACKGROUND

1. Field of the Invention

The present disclosure relates generally to thermal management, and more particularly to devices and methods for transferring heat from a removable module within a chassis.

2. Description of Related Art

High-performance semiconductor devices sometimes produce more waste heat than can be carried away from the device package by thermal radiation, conduction, and/or convection across the device package. Cooling problems may arise due to the power density of the device relative to its cooled surface area, difficulty in providing sufficient coolant flow across the device, and/or due to difficulty in providing a sufficiently large temperature differential between the device package and the coolant flowing across the device. Coolant temperature problems may arise due to the ambient temperature in which a system operates, and/or due to heating of the coolant flow prior to the coolant reaching the device package. Problematic device packages can be fitted with heat sinks and/or secondary cooling fans to assist in removing waste heat.

In some systems, spacing and packaging constraints and or local airflow/air temperature conditions prevent the successful application of a heat sink and/or secondary cooling fan directly to a semiconductor package. In such cases, a thermally conductive “heat pipe” can be fitted to the device package and used to draw heat away from the device package to a remote location. One end of the heat pipe maintains thermal contact with the device package to be cooled; the opposite end of the heat pipe is kept at a lower temperature, e.g., by immersing the second end in a relatively cool fluid stream. The temperature differential between the ends of the heat pipe draws heat away from the device to be cooled.

One difficulty with heat pipes arises when a device to be cooled by the heat pipe is built into a removable module, and the cooling fluid stream used by the heat pipe is located outside the module. In such cases, it may be difficult or even undesirable to design the heat pipe in a way that allows extraction of the heat pipe from the fluid stream and/or system when the module is removed from the system.

FIG. 1 illustrates a prior art cooling apparatus 100 that employs a “partable” thermal heat pipe that is useful, e.g., when the hot end of a heat pipe is located in a removable part of the system and the cool end of the heat pipe is fixed in the system. A bulkhead 110 contains an aperture 112 through which a heat pipe extends. The heat pipe is constructed in two sections 120 and 130. Heat pipe section 120 has one end thermally coupled to a device to be cooled 124, and its other end terminated in a thermal contact plate 122. Heat pipe section 130 has one end terminated in a thermal contact plate 132, and its other end fashioned as a thermal radiator 134, e.g., located in a fluid stream 140. When the system is assembled, thermal contact plates 122 and 132 have their facing sides coated in thermal grease and held in contact with each other, allowing heat transfer between the device 124 and the thermal radiator 134. When the module containing device 124 is to be removed from system 100, heat pipe section 120 is removed through aperture 112, while heat pipe section 130 remains fixed in place.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be best understood by reading the specification with reference to the following Figures, in which:

FIG. 1 illustrates a prior art partable heat pipe in side view;

FIGS. 2, 3, and 4 contain side views of a partable heat pipe according to an embodiment at three stages of coupling;

FIGS. 5 and 6 contain perspective views of two partable heat pipe embodiments;

FIGS. 7 and 8 contain, respectively, side and perspective views of another partable heat pipe embodiment; and

FIGS. 9A and 9B show the FIG. 8 embodiment used in a circuit board that accepts removable electro-optic modules.

DETAILED DESCRIPTION

It has now been discovered that prior art partable heat pipes contain several disadvantageous design features. First, the mating faces on the heat pipe section contact plates must be flat and perfectly parallel in order to maintain effective thermal contact between the two heat pipe sections. Slight misalignments between the two contact plates may sharply curtail the contact area and consequently the heat transfer capability of the heat pipe. Second, the “fully inserted” position of a module containing heat pipe section 120 is determined by the full contact position of the contact plates. In a system that mates electrical connectors through the same insertion sequence that causes contact between the heat pipe contact plates, the full mating of the electrical connectors can be critical to system operation. Thus electrical connectors and heat pipe sections must be critically aligned on both the module and the fixed portion of the system, or else at least one of the electrical and thermal connections will suffer. Third, the contact faces may require a large surface area to lower the thermal impedance of an imperfect (or even perfect) contact position, defeating miniaturization gains elsewhere in the system. Finally, the thermal grease present on the face of the contact plate 122 is subject to contact by a user when a module containing heat pipe 120 is removed from system 100. Not only may the user inadvertently spread thermal grease in places other than that desired, causing annoyance to the user, but the user may inadvertently or purposely remove the grease that is critical to the thermal interface function.

The present disclosure includes low-profile, self-aligning partable heat pipe embodiments that generally can be used to overcome the deficiencies noted above. FIG. 2 contains a cross-section of a first exemplary embodiment 200, prior to joining the two partable heat pipe sections. A fixed member 210, such as a bulkhead, other chassis member, electrical backplane, circuit board, second module, etc., serves as a reference point for the embodiment. A target heat pipe 230 is assembled in a carrier 220, and the carrier 220 is fastened to fixed member 210, e.g., using fasteners 212, 214. A source heat pipe 250 is fixed to a removable module 240. The source heat pipe 250 removes heat from a source device 242, e.g., through a contact section 258 in thermal contact with source device 242 (thermal grease between source device 242 and contact section 258 may be used to improve heat transfer). The target heat pipe 230 transfers the heat to a thermal target, e.g., a thermal radiator 234 located in a cooling fluid stream 202.

Heat transfer between the source heat pipe and the target heat pipe occurs at a partable conical or wedge shaped interface. Source heat pipe 250 includes a female interface element 252 in the form of a hollow cone or wedge with a conical or wedge-shaped inner cavity surface 260. Target heat pipe 230 includes a male interface element 232 in the form of a solid cone or wedge having the same release angle as the inner cavity surface 260. When the source and target heat pipes are brought together (see FIG. 3), the male interface element 232 fits against the inner cavity surface 260 of the female interface element 252 and forms a thermal connection. Thermal grease on the two surfaces (male and female interface surfaces) assists in forming an effective thermal joint.

Several advantages accrue from the use of a cone or wedge interface between the two heat pipes. Depending on the release angle selected (angles between 0.5 degrees and 45 degrees are preferred), the wedge interface can have a substantially lower profile than the flat face interface of the prior art. When combined with the articulation and spring-loading features described below, the wedge interface is also substantially self-aligning due to the complementary forces exerted by the cone or wedge faces. Thermal expansion of the receptacle, if greater than that of the wedge 232 due to higher temperature, merely causes a repositioning of the wedge in the receptacle, but does not decrease the contact area between the wedge and the receptacle or cause the wedge to stick in the receptacle. Thermal grease can be applied to both inner cavity surface 260 and wedge 232. The thermal grease inside receptacle 252 is inaccessible to the user when module 240 is removed from the system (at least for small cavity openings).

Carrier 220 is positioned with respect to an aperture 216, through which target heat pipe 230 passes, in fixed member 210. Carrier positioning nominally aligns target heat pipe 230 with the insertion direction 280 of module 240. A grommet or gasket 222 further positions heat pipe 230 within aperture 216, while providing some environmental sealing between the two sides of fixed member 210, if so desired. Grommet 222 allows target heat pipe 230 to translate along the insertion direction 280, and may also flex to allow minor translation of heat pipe 230 perpendicular to the insertion direction and/or to allow small angular variations in the alignment of target heat pipe 230. Carrier 220 also holds target heat pipe with a relatively loose tolerance that allows the translation and angular variations in the positioning of target heat pipe 230 with respect to fixed member 210.

Heat pipe 230 is spring-loaded to control the holding force between the target heat pipe 230 and source heat pipe 250 over a range of module 240 positions. In FIG. 2, a compression spring 224, placed over a center section of target heat pipe 230, rests between carrier 220 and a collar 236 (which may or may not be flexible) on target heat pipe 230. Spring 224 compresses once wedge 232 is fully inserted in receptacle 252 and further force is applied in the insertion direction 280, such that the contact force remains relatively constant (see FIG. 4, where spring 224 is compressed). Spring-loading keeps an appropriate pressure between the heat pipe sections, lowering alignment tolerances and providing headroom for expansion of the two heat pipe sections with temperature.

FIGS. 2-4 show an insertion sequence that mates the source and target heat pipes, and simultaneously mates a module electrical connector 270 with a fixed electrical connector 272. FIG. 2 shows module 240 separated from the remainder of system 200. In FIG. 3, module 240 has been moved in insertion direction 280 until the target heat pipe wedge is fully contacting inner wedge surface 260. Electrical connectors 270 and 272 have begun to mate, but are not yet fully connected and the spring 224 is not yet compressed. In FIG. 4, electrical connectors 270 and 272 are fully mated, and spring 224 has been compressed.

The inner cavity surface 260 and wedge 232 are designed with a desired number of contact surfaces. FIGS. 5 and 6 show two possible wedge designs in perspective view. FIG. 5 illustrates a source heat pipe 520 with an integrated female receptacle (see the illustrated cavity with inner surface 522), and a target heat pipe 530 with a wedge 532 on one end and a thermal radiator 534 on the opposite end. Wedge 532 is conical, as is the contact surface 522 on the inside of source heat pipe 520.

FIG. 6 illustrates a source heat pipe 620 with an integrated female receptacle (see the illustrated cavity with inner surface 622), and a target heat pipe 630 with a wedge 632 on one end and a thermal radiator 634 on the opposite end. Wedge 632 forms a traditional two-sided wedge, as does the contact surface 622 on the inside of source heat pipe 530. The width of wedge 632 is preferably somewhat smaller than the width of the opening in source heat pipe 620, forming a natural lateral alignment tolerance. Alternately, and particularly useful with larger release angles on the top and bottom surfaces, the sides of the wedge and opening can also be wedge-shaped and designed to contact when the source heat pipe and target heat pipe are in full contact.

FIGS. 7 and 8 illustrate respectively in side and perspective views, an alternate partable heat pipe embodiment 700. The source heat pipe is a flattened metal member 710 with an opening 712 in one end. The target heat pipe 720 includes a flattened wedge 722 on one end, integral cooling fins along the bulk of the heat pipe, and a spring/support cantilever section 724 on the end opposite the wedge 722. The free end of cantilever 724 can be fixed to a desired support. Opening 712 includes an enlarged recess, with the wedge contact surface set back into the opening to further contain the thermal grease.

One use for embodiment 700 is to provide cooling for a compact form-factor electro-optic module that provides network connectivity to a computer, router, switch, etc. Such modules typically contain semiconductor lasers and drivers, receivers, and interface electronics in a small module package. The module can generate a substantial amount of waste heat, but the heat may be difficult to remove due to interference from the cage that holds the module and/or close proximity to similar modules that impede airflow.

FIGS. 9A and 9B illustrate the use of a partable heat pipe such as embodiment 700 to cool a compact form-factor electro-optic module. FIG. 9A depicts an embodiment 900 consisting of pluggable optic module 910 and an interface card 930. Different versions of pluggable optic module 910 can support, in the same form factor, different optical (or copper) physical interface standards or wavelengths externally, and a common electrical interface to interface card 930 internally. The top surface of module 910 is at least partially formed from a source heat pipe 920. The internal heat-generating components of module 910 preferably thermally couple to the lower surface of heat pipe 920. The rear end of heat pipe 920 contains an opening (not visible) of the type shown as opening 712 in FIGS. 7 and 8.

Interface card 930 includes a substrate that is or includes a printed circuit board. A module cage 932, fixed to the printed circuit board, includes electrical connectors for providing signal/power connectivity between module 910 and supporting electronics on card 930. The module cage 932 also provides mechanical features to engage and hold module 910 when the module is inserted in the cage.

A target heat pipe 940 includes a heat transfer wedge 942, coated in thermal grease, integral cooling fins, and a spring/support 944. Spring support 944 fixes to card 930 at a position behind cage 932, such that the heat transfer wedge is cantilevered over the cage 932 in nominal alignment with the inserted position of source heat pipe 920.

FIG. 9B shows an assembled view of embodiment 900. Heat from the internal heat-generating components of module 910 is transferred to source heat pipe 920, through the wedge interface between source heat pipe 920 and target heat pipe 940, and then to a cooling air stream through the cooling fins of the target heat pipe 940. Spring/support 944 maintains positive thermal contact for the wedge interface. If so desired, spring/support 944 can also transfer a latch release force to module 910 through the source heat pipe 920. When a module release trigger is activated, spring/support 944 pushes the module to an unlatched position to facilitate removal.

Those skilled in the art will appreciate that the embodiments and/or various features of the embodiments can be combined in other ways than those described. For instance, although spring/support 944 is shown connected directly to a horizontal circuit board, the support can alternately connect to a vertical member or to an integral portion of the module cage. Various other locations for a spring means are possible and comprehended as within the scope of the disclosure. Other variations on the number of wedge contact surfaces are possible. The release angles of each surface need not be the same. The wedge need not come to a point. The source heat pipe may also comprise cooling and/or heat capture fins.

Although the specification may refer to “an”, “one”, “another”, or “some” embodiment(s) in several locations, this does not necessarily mean that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. 

1. A self-aligning partable heat pipe comprising: a source section attached to a removable electronic module, the distal end of the source section in thermal contact with a heat source and the proximal end of the source section forming a female interface element; a target section passes through and is retained by both of an aperture in a fixed member and an aperture in a carrier member and is able to translate towards and away from an insertion direction of the removable electronic module, and the target section includes a thermal target and a proximal end of the target section forms a male interface element; and the female interface element of the source section and the male interface element of the target section together comprise a partable, self-aligning thermally conductive interface through which heat from the heat source is transferred to the thermal target.
 2. The thermally conductive interface of claim 1, wherein the female interface element is comprised of a hollow wedge shaped receptacle and the male interface element is comprised of a solid wedge that fits inside the hollow wedge shaped receptacle of the female interface element.
 3. The female interface element of claim 2, wherein the hollow wedge shaped receptacle is comprised of an inner cavity surface and the sides are wedge shaped.
 4. The male interface element of claim 2, wherein the wedge is a two-sided wedge and the width of the wedge is smaller than the opening in the female interface element.
 5. The wedge shaped form of claim 4, wherein the sides of the wedge are wedge-shaped.
 6. The female interface element of claim 2, wherein the wedge is conical.
 7. The male interface element of claim 2, wherein the wedge is conical.
 8. The partable heat pipe of claim 1, wherein the removable electronic module is a printer circuit board.
 9. The partable heat pipe of claim 1, wherein the heat source is an electronic device.
 10. The partable heat pipe of claim 1, wherein the fixed member is any one of a bulkhead, other chassis member, electrical backplane, circuit board and second module.
 11. The partable heat pipe of claim 1, wherein the carrier member is fastened to the fixed member.
 12. The partable heat pipe of claim 1, wherein the thermal target is a thermal radiator.
 13. The partable heat pipe of claim 1, wherein the target section is spring loaded.
 14. The hollow wedge shaped receptacle of claim 3, wherein the inner cavity surface is coated with thermal grease. 